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Thomas Schwager

Publications and source records attributed to Thomas Schwager.

23 records · Page 2Linked to original sources
arXiv2002

Vertically shaken column of spheres. Onset of fluidization

The onset of surface fluidization of granular material in a vertically vibrated container, z=A cos(ωt), is studied experimentally. Recently, for a column of spheres it has been theoretically found that the particles lose contact if a certain condition for the acceleration amplitude \ddot{z} \equiv Aω^2/g = f(ω) holds. This result is in disagreement with other findings where the criterion \ddot{z}=\ddot{z}_{crit}=const. was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not a proper criterion for fluidization and compare the results with theory.

cond-mat.mtrl-sci↗
arXiv1999

Onset of fluidization in vertically shaken granular material

When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation and other effects. There is a controversial discussion in literature whether there exists a threshold for the Froude number $Γ=A_0ω_0^2/g$ below which these effects cannot be observed anymore. By means of theoretical analysis and computer simulation we find that there is no such single threshold. Instead we propose a modified criterion which coincides with critical Froude number $Γ_c=1$ for small driving frequency $ω_0$.

cond-mat.stat-mech↗
arXiv1999

Coefficient of restitution of colliding viscoelastic spheres

We perform a dimension analysis for colliding viscoelastic spheres to show that the coefficient of normal restitution $ε$ depends on the impact velocity g as ε=1-γ_1g^{1/5}+γ_2g^{2/5}\mp..., in accordance with recent findings. We develop a simple theory to find explicit expressions for coefficients γ_1 and γ_2. Using these and few next expansion coefficients for ε(g) we construct a Padé-approximation for this function which may be used for a wide range of impact velocities where the concept of the viscoelastic collision is valid. The obtained expression reproduces quite accurately the existing experimental dependence ε(g) for ice particles.

cond-mat.stat-mech↗
arXiv1998

Rolling friction of a hard cylinder on a viscous plane

The resistance against rolling of a rigid cylinder on a flat viscous surface is investigated. We found that the rolling-friction coefficient reveals strongly non-linear dependence on the cylinder's velocity. For low velocity the rolling-friction coefficient rises with velocity due to increasing deformation rate of the surface. For larger velocity, however, it decreases with velocity according to decreasing contact area and deformation of the surface.

cond-mat.mtrl-sci↗